Surface Photo-Voltage Spectroscopy: A Versatile Technique …
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successfully attribute these strong illumination dependence of the two mechanisms
to the trap controlled mobility of charge-carriers in the samples.
Thus, the illumination intensity could be one more useful variables in the
SPS to understand the charge-generation and charge transfer mechanisms in the
semiconductor materials and devices.
4.4 Temperature Dependence of SPS
Another very important measurement variable in the SPS is temperature. Since the
charge carrier generation and re-distribution are strong function of temperature,
taking SPS measurements under different temperature conditions could provide a
much more comprehensive view of the physics of materials being probed. It must
be noted that the temperatures affect the SPV in a number of ways. For example,
the SPV generation relies on optical transitions which take place in the background
of the thermal noise. Hence, many feeble features in SPV may not be visible at
room temperatures. However, reducing temperature may allow observance of such
features. Also, the subsequent to the generation of charge carriers upon illumination,
their mobilities in bulk as well as at interface depend strongly on the temperature of
the samples, which consequently affect the observed SPV spectra. Thus, knowing
the temperature dependent variation of SPV features in the spectra may allow us
to extract quite a few interesting information. Further, the MIS configuration with
chopped light mode is relatively easy to implement in any typical cryostat, allowing
the measurements in a wide range of temperatures.
There are large number of reports on temperature dependent SPS on a wide variety
of samples. Chan et al. have reported an extensive study on temperature dependence
of SPS on a series of vertically stacked self-organized InAs/GaAs quantum dot (QD)based laser structures with different spacer layer (SL) thickness [80]. They measured
the SPV spectra in a temperature range from 77 K to 300 K. They attribute the low
SPV signals at higher temperatures to the inefficient carrier transport due to lattice
scattering in view of increased concentration of phonons [81]. The reduced SPV at
the lower end of the temperature range in case of thicker spacer layers is explained
by the built-in electric field and the relevant escape efficiency of carriers at the low
temperatures [82]. However for the thinner spacer layer, they don’t observe very low
SPV at low temperatures, which is proposed to be a direct evidence of the tunneling
through thin space layer. Datta et al. have also reported investigations on temperature
dependent SPS results on bulk III-V materials [83]. They have explained their SPS
results and their dependence on operating temperature by applying Schottky based
model. The model is proposed to be able to explain the data well if the junction
non-idealities are appropriately taken into account.
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successfully attribute these strong illumination dependence of the two mechanisms
to the trap controlled mobility of charge-carriers in the samples.
Thus, the illumination intensity could be one more useful variables in the
SPS to understand the charge-generation and charge transfer mechanisms in the
semiconductor materials and devices.
4.4 Temperature Dependence of SPS
Another very important measurement variable in the SPS is temperature. Since the
charge carrier generation and re-distribution are strong function of temperature,
taking SPS measurements under different temperature conditions could provide a
much more comprehensive view of the physics of materials being probed. It must
be noted that the temperatures affect the SPV in a number of ways. For example,
the SPV generation relies on optical transitions which take place in the background
of the thermal noise. Hence, many feeble features in SPV may not be visible at
room temperatures. However, reducing temperature may allow observance of such
features. Also, the subsequent to the generation of charge carriers upon illumination,
their mobilities in bulk as well as at interface depend strongly on the temperature of
the samples, which consequently affect the observed SPV spectra. Thus, knowing
the temperature dependent variation of SPV features in the spectra may allow us
to extract quite a few interesting information. Further, the MIS configuration with
chopped light mode is relatively easy to implement in any typical cryostat, allowing
the measurements in a wide range of temperatures.
There are large number of reports on temperature dependent SPS on a wide variety
of samples. Chan et al. have reported an extensive study on temperature dependence
of SPS on a series of vertically stacked self-organized InAs/GaAs quantum dot (QD)based laser structures with different spacer layer (SL) thickness [80]. They measured
the SPV spectra in a temperature range from 77 K to 300 K. They attribute the low
SPV signals at higher temperatures to the inefficient carrier transport due to lattice
scattering in view of increased concentration of phonons [81]. The reduced SPV at
the lower end of the temperature range in case of thicker spacer layers is explained
by the built-in electric field and the relevant escape efficiency of carriers at the low
temperatures [82]. However for the thinner spacer layer, they don’t observe very low
SPV at low temperatures, which is proposed to be a direct evidence of the tunneling
through thin space layer. Datta et al. have also reported investigations on temperature
dependent SPS results on bulk III-V materials [83]. They have explained their SPS
results and their dependence on operating temperature by applying Schottky based
model. The model is proposed to be able to explain the data well if the junction
non-idealities are appropriately taken into account.